Restaurant waiters and other workers who earn most of their money from tips are only entitled to a $2.13 hourly wage from their employers, according to federal law. Now, a group of them are suing, saying they should be paid a regular hourly wage for all the work they do that doesn't bring in tips, like sweeping floors.

On Thursday, a federal court heard arguments in a case that could have consequences for all employers who pay tipped workers less than minimum wage. In Arizona, three servers at Chinese-themed restaurant P.F. Chang's and a server at Village Inn argue that they're owed full hourly wages for time spent preparing food and cleaning, work for which they do not receive tips. The two companies did not respond to requests for comment Friday.

While a Congressional definition says workers who "customarily receive more than $30 a month in tips" can be paid the federal tipped minimum wage, a separate guide published by the Labor Department says people who spend more than 20% of their time on non-tipped work should receive full wages for that time.

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The servers in the case recount spending more than 20% of their time on non-tipped work like scrubbing walls, cleaning seats, refilling salt and pepper shakers, brewing tea and coffee, and rolling silverware. They allege that their employers have violated the Fair Labor Standards Act by denying them full pay for that time worked. A lower court dismissed the claims, which they then appealed.

P.F. Chang’s argued that the classification of a tipped worker as someone who receives more than $30 a month in tips is the key definition, and that the Labor Department handbook is inconsistent with the intent of law.

Should the court rule in favor of the workers, not only will they receive back pay, but other tipped workers who are tasked with non-tipped work may qualify for financial relief for time worked as well.

The Department of Labor has filed an amicus brief in the case in support of the 20% interpretation.